Circuit arrangement for operating electric arc discharge devices

ABSTRACT

Electric arc discharge device operating apparatus includes rectifier means and an inverter circuit connected to said input terminals and having first and second output terminals. An autotransformer has a main winding across which is connected a capacitor. A drive transformer has a core of linear low loss characteristics, a primary winding and two secondary windings. The primary winding is connected across a portion of the main autotransformer winding between one terminal and an adjacent tap, and each secondary winding is connected to the control terminal of one of the inverter switching devices. The saturation characteristics of the drive transformer are coordinated with the saturation characteristics of the autotransformer so that drive transformer saturation causes switching of the inverter circuit switching devices without saturation of the autotransformer.

United States Patent Crane 1 Oct. 30, 1973 Primary Examiner-Roy Lake Assistant Examiner-Lawrence J. Dahl Attorney-Willis M. Ertman [57] ABSTRACT Electric arc discharge device operating apparatus includes rectifier means and an inverter circuit connected to said input terminals and having first and second output terminals. An autotransformer has a main winding across which is connected a capacitor. A drive transformer has a core of linear low loss charac teristics, a primary winding and two secondary windings. The primary winding is connected across a portion of the main autotransformer winding between one terminal and an adjacent tap, and each secondary winding is connected to the control terminal of one of the inverter switching devices. The saturation characteristics of the drive transformer are coordinated with the saturation characteristics of the autotransformer so that drive transformer saturation causes switching of the inverter circuit switching devices without saturation of the autotransformer.

17 Claims, 3 Drawing Figures IIO/ no no no CIRCUIT ARRANGEMENT FOR OPERATING ELECTRIC ARC DISCHARGE DEVICES SUMMARY OF INVENTION This invention relates to circuit arrangements for operating electric arc discharge devices.

The starting and operation of arc discharge devices such as fluoroescent lamps and high pressure mercury lamps presents two major problems. Such devices require a relatively high voltage to ignite an arc as compared with the voltage needed to maintain the arc once it has been ignited. Secondly, the ignited arc has a negative resistance characteristic, so that it tends to draw increasing amounts of current. Resistive and inductive ballast arrangements have been provided for use with such devices and are designed to produce a peak voltage adequate to strike the arc and then limits the current through the arc. Such ballasts are heavy, bulky, expensive to make and draw substantial power. Further, unless carefully constructed, inductive ballasts generate objectionable acoustic and electromagnetic noise.

Accordingly, it is an object of this invention to provide a novel and improved arc discharge control circuit particularly useful with arc discharge devices such as fluoroescent lamps.

In accordance with the invention there is provided electric arc discharge device operating apparatus that includes input terminals for direct connection to an alternating power source. Rectifier means is connected to the input terminals and has first and second output terminals. A main transformer has a core of linear low loss material on which is wound a plurality of winding portions. In a preferred embodiment the main transformer is an autotransformer and its main winding has first and second taps. First circuit means connects one rectifier output terminal to the first autotransformer winding tap. An inverter circuit in a preferred embodiment has a pair of transistors with their emitter electrodes connected together through ballast resistors. The collector electrode of one transistor is connected to one terminal of the main autotransformer winding, and the collector electrode of the other transistor is connected to the second tap. A drive transformer has a saturable core having linear, low loss characteristics, on which is wound a primary winding and two secondary windings. The drive transformer core cross-section in a preferred embodiment is less than one tenth the main transformer core cross-section. Its primary winding is connected across a portion of the autotransformer main winding. One of the drive transformer secondary windings is connected to the control electrode of one inverter switching device, and the second drive transformer secondary winding is connected to the control electrode of the other inverter switching device. The apparatus includes a series of pairs of output terminals and inductors are connected between the main autotransformer winding and one output terminal of each pair and an electric arc discharge device may be connected between a pair of output terminals in circuit across the main autotransformer winding.

In a particular embodiment, the emitter electrodes of the inverter transistors are each connected in series with a ballast resistor having a value of less than ohms to a common junction point and imbalance means is connected to the base electrodes of one of the transistors for initiating operation of the circuits. The output terminals are arranged for connecting a plurality of pairs of fluoroescent lamps across the autotransformer main winding, each pair of lamps being connected in series with an inductor having a value of less than 50 millihenries. A capacitor is also connected across the main winding and coordinated with the inductive value of the main winding to modify its rate of voltage change. The core of the main transformer is of toroid configuration and has a cross-section that is substantially greater than the cross-section of the core of the drive transformer. Surge protector means is connected across the input terminals of the rectifier means.

The invention provides an efficient, compact circuit for operating arc discharge devices such as fluoroescent lamps directly from an alternating power source. Other objects, features and advantages will be seen as the following description of a particular embodiment progresses, in conjunction with the drawings in which:

FIG. 1 is a schematic diagram of a circuit constructed in accordance with the invention;

FIG. 2 is a hysteresis curve indicating characteristics of the drive transformer core; and

FIG. 3 are graphical representations illustrating the relationships between waveform characteristics of the circuit shown in FIG. 1.

DESCRIPTION OF PARTICULAR EMBODIMENT The circuit shown in FIG. 1 includes terminals 10, 12 adapted for connection to a l20-volt alternating power source. A gas discharge type of surge protector 14 is connected across terminals 10 and 12. Also connected across terminals 10 and 12 is a full wave rectifier 16 that includes four diodes 18 and has output terminals 20, 22 across which is supplied a ISO-volt signal. Filter capacitor 24 is connected across rectifier output terminals 20 and 22.

The circuit also includes an autotransformer 26 having a toroidal core of linear low loss (Ferrox cube 3E ferrite) material on which is wound a main winding 30 that has a first tap 32 and a second tap 34 so that the same voltage (150 volts) is provided from the winding section between terminal 36 and tap 32 and from the section of the transformer winding between taps 32 and 34. The additional winding section between tap 32 and terminal 38 provides an output voltage of approximately 350 volts between terminals 36 and 38. Connected across terminals 36 and 38 is capacitor 40 whose value is coordinated with the inductive value (20 henries) of the autotransformer. A small inductor 42 is connected between terminal 36 and each output terminal 44. Auxiliary windings 50 that are coupled to autotransformer winding 30 through core 28 provide lamp filament power.

Connected between rectifier 16 and autotransformer 30 is a two-transistor inverter circuit that includes two high voltage switching transistors 60, 62 (e.g., RCA type 2N5840 or Delco type DTS 402), each transistor having a base electrode 64, an emitter electrode 66 and a collector electrode 68. A diode 70 is connected across the emitter electrode 66 and collector electrode 68 of each transistor to limit reverse current flow in the output circuit of the transistor. Connected to the base electrode of each transistor is a resistor 72. The emitter electrodes 66 of the two transistors 60, 62 are connected via ballast resistors 74 to junction 76 and that junction is connected to terminal 22 of rectifier 16. Imbalance capacitor 82 is connected between the input circuit of transistor 62 and terminal 12.

The system further includes a drive transformer having a core 90 composed of a pair of members of much smaller cross-section than core 28, one of which is of E configuration and both of which are of linear low loss ferrite that has a characteristic as indicated in FIG. 2 '(e.g., Ferrox cube 3E material) on which is wound a primary winding 92 that is connected in series with resistor 94 between terminal 38 of autotransformer winding 30 and tap 32; a first secondary winding 96 and a second secondary winding 98. The turns ratio of primary winding 92 to each secondary winding is 7:1. One terminal of each secondary winding 96, 98 is connected to terminal 22 of rectifier 16 at junction 100 via diodes 102. The second terminal of secondary winding 96 is connected through the input circuit to base electrode 64 of transistor 72 while the second terminal of the secondary winding 98 is similarly connected to base electrode 64 of transistor 60.

This ballast circuit is arranged to drive electric arc discharge devices such as fluoroescent lamps 110. Two such lamps 110 may be connected in series across terminals 42 and 44 and several such pairs of lamps may be connected in parallel as indicated in FIG. 1.

In operation, rectifier l6 rectifies the incoming AC current with capacitor 24 providing filtering at 60 hertz and increased filtering at frequencies above several thousand hertz, the inverter operating at 20 kHz. When power is applied to terminals 10, 12, a slight inbalance in biasing due to capacitor 82 causes transistor 72 to conduct first. As a result of such conduction, a voltage is induced across the section of the autotransformer winding 30 between taps 32 and 34, supplying electric current which in turn induces a voltage across output terminals 44, 46. The voltage in autotransformer winding 30 is also applied to primary winding 92 of the drive transformer 90. Drive transformer secondary winding 96 is connected in circuit with transistor 62 and its output drives that transistor into saturation. The circuit remains in this state only until core 90 of the drive transformer saturates. This saturation terminates the drive to transistor 62 and causes it to stop conducting. The magnetic fields in the autotransformer 26 and in the drive transformer then rapidly collapse, inducing a voltage of opposite polarity in the secondary windings 96, 98. The voltage induced in secondary winding 98 causes transistor 60 to start conducting and that transistor is rapidly driven to saturation and remains in that state until the core 90 of the control transformer again saturates in the opposite direction. At this time transistor 60 turns off. This operation repeats cyclically, the components values being sleected so thac the frequency of the operation is in the range of 20 kHz, and the circuitry provides an output current at terminals 44, 46 in the order of 420 milliamperes magnitude to operate the fluoroescent lamps 110.

Waveforms indicating operation characteristics of the circuit are shown in FIG. 3. FIG. 30 indicates the waveform of the voltage in the primary winding 92 of drive transformer 90; FIG. 3b indicates the VCE waveform of one of the transistors 60, 62 with the output voltage waveform of the other transistor being 180 out of phase; FIG. 30 indicates the collector current (Ic) of the same transistor; FIG. 3d indicates the base current (lb) of that same transistor; FIG. 3e indicates the waveform of current flowing through bulbs 1 and FIG. 3f indicates the waveform of the voltage across a bulb 1 10. It will be noted that the bulb current (FIG. 3e) approaches sine wave form and as such provides increased bulb life.

The invention provides a compact, economical, efficient and light weight drive for multiple arc discharge devices. While a particular embodiment of the invention has been shown and described, various modifications thereof will be apparent to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiments or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. Electric arc discharge device operating apparatus comprising:

input terminals for direct connection to an alternating power source, rectifier means connected to said input terminals and having first and second output terminals,

autotransformer means having a core and a main winding on said core, said main winding having two terminals and two taps,

and further including a capacitor connected across said main winding and coordinated with the inductive value of said main winding to modify the rate of voltage change, an inverter circuit comprising a pair of solid state switching devices, each said switching device having a control terminal and an output terminal,

first circuit means connecting the output terminal of one of said switching devices to one terminal of said autotransformer main winding,

second circuit means connecting the output terminal of the other switching device to a tap of said autotransformer main winding,

third circuit means connecting one output terminal of said rectifier means to another tap of said main winding,

a drive transformer having a core of linear low loss characteristics, and

a primary winding and two secondary windings on said drive transformer core,

fourth circuit means connecting said primary winding across a portion of said main autotransformer winding,

fifth circuit means connecting one drive transformer secondary winding to the control terminal of one of said switching devices,

sixth circuit means connecting the other drive transformer secondary winding to the control terminal of the other switching device, said drive transformer and said fifth and sixth circuit means causing said switching devices of said inverter circuit to switch conducting states in response to saturation of said drive transformer core,

the saturation characteristics of said drive transformer being coordinated with the saturation characteristics of said autotransformer so that said drive transformer saturation causes switching of said inverter circuit switching devices without saturation of said autotransformer core,

and output terminal means for connecting an electric arc discharge device across said autotransformer main winding.

2. The apparatus as claimed in claim 1 wherein said switching devices are transistors, each of which has base, emitter and collector electrodes, and further including means including a resistor having a value of less than ohms connecting each emitter electrode to a common junction point.

3. The apparatus as claimed in claim 1 and further including a capacitor connected across said main winding and coordinated with the inductive value of said main winding to modify the rate of voltage change, and a plurality of output inductors connected to one terminal of said transformer main winding, each said output indictor having an inductive value of less than 50 millihenries.

4. The apparatus as claimed in claim 1 wherein said drive transformer has a step down turns ratio.

5. The apparatus as claimed in claim 1 and further including imbalance means connected to the input terminal of one of said switching devices for initiating operation of said inverter circuit.

6. The apparatus as claimed in claim 1 and further including surge protector means connected across the input terminals of said rectifier means.

7. The apparatus as claimed in claim 1 wherein said output terminal means includes means for connecting a plurality of fluoroescent lamps across said autotransformer main winding and further including plurality of secondary windings coupled to the autotransformer for connection to filaments of the lamps.

8. The apparatus as claimed in claim 1 wherein said cross-section of said drive transformer core is substantially smaller than the cross-section of said main transformer core.

9. The apparatus as claimed in claim 8 wherein said switching devices are transistors, each of which has base, emitter and collector electrodes, and further including means including a resistor having a value of less than five ohms connecting each emitter electrode to a common junction point, and imbalance means connected to the base electrode of one of said transistors for initiating operation of said inverter circuit.

10. The apparatus as claimed in claim 1 wherein said output terminal means includes means for connecting a plurality of fluoroescent lamps across said autotransformer main winding and further including a plurality of secondary windings coupled to the autotransformer for connection to filaments of the lamps, a capacitor connected across said main winding and coordinated with the inductive value of said main winding to modify the rate of voltage change, a plurality of output inductors connected to one terminal of said transformer main winding, each said output inductor having an inductive value of less than millihenries.

11. Electric arc discharge device operating apparatus comprising:

input terminals for direct connection to an alternating power source,

rectifier means connected to said input terminals and having first and second output terminals,

main transformer means having a core and a plurality of winding portions on said core,

an inverter circuit comprising a pair of switching devices, each said switching device having a control terminal and an output terminal,

first circuit means connecting the output terminals of said switching devices to one transformer winding portion,

second circuit means connecting one output terminal of said rectifier means to said one transformer winding portion,

a drive transformer having a core of linear low loss characteristics, and

a primary winding and two secondary windings on said drive transformer core,

third circuit means connecting said primary winding to a second transformer winding portion,

fourth circuit means connecting one drive transformer secondary winding to the control terminal of one of said switching devices,

fifth circuit means connecting the other drive transformer secondary winding to the control terminal of the other switching device,

said drive transformer and said fourth and fifth circuit means causing said switching devices of said inverter circuit to switch between cutoff and fully conducting states in response to saturation of said drive transformer core,

the saturation characteristics of said drive transformer being coordinated with the saturation characteristics of said main transformer so that said drive transformer saturation causes switching of said inverter circuit switching devices without saturation of said main transformer core,

and output terminal means for connecting an electric arc discharge device across a main transformer winding portion.

12. The apparatus as claimed in claim 11 wherein said switching devices are transistors, each of which has base, emitter and collector electrodes, and further including means including a resistor having a value of less than ten ohms connecting each emitter electrode to a common junction point.

13. The apparatus as claimed in claim 11 wherein said output terminal means includes means for connecting a plurality of fluoroescent lamps across a transformer winding portion and further including a plurality of secondary windings coupled to said main transformer for connection to filaments of the lamps and a plurality of output inductors connected between one of said main transformer winding portions and said output terminal means.

14. Electric arc discharge device operating apparatus comprising:

input terminals for direct connection to an alternating power source,

rectifier means connected to said input terminals and having first and second output terminals,

main transformer means having a core and a plurality of winding portions on said core,

an inverter circuit comprising a pair of switching devices, each said switching device having a control terminal and an output terminal,

first circuit means connecting the output terminals of said switching devices to one transformer winding portion,

second circuit means connecting one output terminal of said rectifier means to said one transformer winding portion,

a drive transformer having a core of linear low loss characteristics, and

a primary winding and two secondary windings on said drive transformer core,

third circuit means connecting said primary winding to a second transformer winding portion,,

fourth circuit means connecting one drive transformer secondary winding to the control terminal of one of said switching devices,

fifth circuit means connecting the other drive transformer secondary winding to the control terminal of the other switching device,

said drive transformer and said fourth and fifth circuit means causing said switching devices of said inverter circuit to switch between cutoff and fully conducting states in response to saturation of said drive transformer core,

the saturation characteristics of said drive transformer being coordinated with the saturation characteristics of said main transformer so that said drive transformer saturation causes switching of said inverter circuit switching devices without saturation of said main transformer core,

and an output inductor connected between one of said main transformer winding portions and said output terminal means.

15. Electric arc discharge device operating apparatus comprising:

input terminals for direct connection to an alternating power source,

rectifier means connected to said input terminals and having first and second output terminals,

main transformer means having a core and a plurality of winding portions on said core,

an inverter circuit comprising a pair of switching devices, each said switching device having a control terminal and an output terminal,

first circuit means connecting the output terminals of said switching devices to one transformer winding portion,

second circuit means connecting one output terminal of said rectifier means to said one transformer winding portion,

a drive transformer having a core of linear low loss characteristics, the cross-section of said drive transformer core being less than one tenth the cross-section of said main transformer core, and

a primary winding and two secondary windings on said drive transformer core,

third circuit means connecting said primary winding to a second transformer winding portion,

fourth circuit means connecting one drive transformer secondary winding to the control terminal of one of said switching devices, fifth circuit means connecting the other drive transformer secondary winding to the control terminal of the other switching device, said drive transformer and said fourth and fifth circuit means causing said switching devices of said inverter circuit to switch between cutoff and fully conducting states in response to saturation of said drive transformer core, 7

the saturation characteristics of said drive transformer being coordinated with the saturation characteristics of said main transformer so that said drive transformer saturation causes switching of said inverter circuit switching devices without saturation of said main transformer core,

and output terminal means for connecting an electric arc discharge device across a main transformer winding portion.

16. The apparatus as claimed in claim 15 wherein said switching devices are transistors, each of which has base, emitter and collector electrodes, and further including means including a resistor having a value of less than five ohms connecting each emitter electrode to a common junction point, and imbalance means connected to the base electrode of one of said transistors for initiating operation of said inverter circuit.

17. The apparatus as claimed in claim 16 wherein said output terminal means includes means for connecting a plurality of fluoroescent lamps across a main transformer winding and further including a plurality of secondary windings coupled to said main transformer for connection to filaments of the lamps, a capacitor connected across said main winding and coordinated with the inductive value of said main winding to modify the rate of voltage change, a plurality of output inductors connected to one terminal of said transform er main winding, each said outputinductor having an inductive value of less th an 20 millihenries. 

1. Electric arc discharge device operating apparatus comprising: input terminals for direct connection to an alternating power source, rectifier means connected to said input terminals and having first and second output terminals, autotransformer means having a core and a main winding on said core, said main winding having two terminals and two taps, and further including a capacitor connected across said main winding and coordinated with the inductive value of said main winding to modify the rate of voltage change, an inverter circuit comprising a pair of solid state switching devices, each said switching device having a control terminal and an output terminal, first circuit means connecting the output terminal of one of said switching devices to one terminal of said autotransformer main winding, second circuit means connecting the output terminal of the other switching device to a tap of said autotransformer main winding, third circuit means connecting one output terminal of said rectifier means to another tap of said main winding, a drive transformer having a core of linear low loss characteristics, and a primary winding and two secondary windings on said drive transformer core, fourth circuit means connecting said primary winding across a portion of said main autotransformer winding, fifth circuit means connecting one drive transformer secondary winding to the control terminal of one of said switching devices, sixth circuit means connecting the other drive transformer secondary winding to the control terminal of the other switching device, said drive transformer and said fifth and sixth circuit means causing said switching devices of said inverter circuit to switch conducting states in response to saturation of said drive transformer core, the saturation characteristics of said drive transformer being coordinated with the saturation characteristics of said autotransformer so that said drive transformer saturation causes switching of said inverter circuit switching devices without saturation of said autotransformer core, and output terminal means for connecting an electric arc discharge device across said autotransformer main winding.
 2. The apparatus as claimed in claim 1 wherein said switching devices are transistors, each of which has base, emitter and collector electrodes, and further including means including a resistor having a value of less than 10 ohms connecting each emitter electrode to a common junction point.
 3. The apparatus as claimed in claim 1 and further including a capacitor connected across said main winding and coordinated with the inductive value of said main winding to modify the rate of voltage change, and a plurality of output inductors connected to one terminal of said transformer main winding, each said output inductor having an inductive value of less than 50 millihenries.
 4. The apparatus as claimed in claim 1 wherein said drive transformer has a step down turns ratio.
 5. The apparatus as claimed in claim 1 and further including imbalance means connected to the input terminal of one of said switching devices for initiating operation of said inverter circuit.
 6. The apparatus as claimed in claim 1 and further including surge protector means connected across the input terminals of said rectifier means.
 7. The apparatus as claimeD in claim 1 wherein said output terminal means includes means for connecting a plurality of fluoroescent lamps across said autotransformer main winding and further including plurality of secondary windings coupled to the autotransformer for connection to filaments of the lamps.
 8. The apparatus as claimed in claim 1 wherein said cross-section of said drive transformer core is substantially smaller than the cross-section of said main transformer core.
 9. The apparatus as claimed in claim 8 wherein said switching devices are transistors, each of which has base, emitter and collector electrodes, and further including means including a resistor having a value of less than five ohms connecting each emitter electrode to a common junction point, and imbalance means connected to the base electrode of one of said transistors for initiating operation of said inverter circuit.
 10. The apparatus as claimed in claim 1 wherein said output terminal means includes means for connecting a plurality of fluoroescent lamps across said autotransformer main winding and further including a plurality of secondary windings coupled to the autotransformer for connection to filaments of the lamps, a capacitor connected across said main winding and coordinated with the inductive value of said main winding to modify the rate of voltage change, a plurality of output inductors connected to one terminal of said transformer main winding, each said output inductor having an inductive value of less than 20 millihenries.
 11. Electric arc discharge device operating apparatus comprising: input terminals for direct connection to an alternating power source, rectifier means connected to said input terminals and having first and second output terminals, main transformer means having a core and a plurality of winding portions on said core, an inverter circuit comprising a pair of switching devices, each said switching device having a control terminal and an output terminal, first circuit means connecting the output terminals of said switching devices to one transformer winding portion, second circuit means connecting one output terminal of said rectifier means to said one transformer winding portion, a drive transformer having a core of linear low loss characteristics, and a primary winding and two secondary windings on said drive transformer core, third circuit means connecting said primary winding to a second transformer winding portion, fourth circuit means connecting one drive transformer secondary winding to the control terminal of one of said switching devices, fifth circuit means connecting the other drive transformer secondary winding to the control terminal of the other switching device, said drive transformer and said fourth and fifth circuit means causing said switching devices of said inverter circuit to switch between cutoff and fully conducting states in response to saturation of said drive transformer core, the saturation characteristics of said drive transformer being coordinated with the saturation characteristics of said main transformer so that said drive transformer saturation causes switching of said inverter circuit switching devices without saturation of said main transformer core, and output terminal means for connecting an electric arc discharge device across a main transformer winding portion.
 12. The apparatus as claimed in claim 11 wherein said switching devices are transistors, each of which has base, emitter and collector electrodes, and further including means including a resistor having a value of less than ten ohms connecting each emitter electrode to a common junction point.
 13. The apparatus as claimed in claim 11 wherein said output terminal means includes means for connecting a plurality of fluoroescent lamps across a transformer winding portion and further including a plurality of secondary windings coupled to said main transformer for connection to filaments of the lamps and a plurality of output inductors connected between one of said main transformer winding portions and said output terminal means.
 14. Electric arc discharge device operating apparatus comprising: input terminals for direct connection to an alternating power source, rectifier means connected to said input terminals and having first and second output terminals, main transformer means having a core and a plurality of winding portions on said core, an inverter circuit comprising a pair of switching devices, each said switching device having a control terminal and an output terminal, first circuit means connecting the output terminals of said switching devices to one transformer winding portion, second circuit means connecting one output terminal of said rectifier means to said one transformer winding portion, a drive transformer having a core of linear low loss characteristics, and a primary winding and two secondary windings on said drive transformer core, third circuit means connecting said primary winding to a second transformer winding portion,, fourth circuit means connecting one drive transformer secondary winding to the control terminal of one of said switching devices, fifth circuit means connecting the other drive transformer secondary winding to the control terminal of the other switching device, said drive transformer and said fourth and fifth circuit means causing said switching devices of said inverter circuit to switch between cutoff and fully conducting states in response to saturation of said drive transformer core, the saturation characteristics of said drive transformer being coordinated with the saturation characteristics of said main transformer so that said drive transformer saturation causes switching of said inverter circuit switching devices without saturation of said main transformer core, and an output inductor connected between one of said main transformer winding portions and said output terminal means.
 15. Electric arc discharge device operating apparatus comprising: input terminals for direct connection to an alternating power source, rectifier means connected to said input terminals and having first and second output terminals, main transformer means having a core and a plurality of winding portions on said core, an inverter circuit comprising a pair of switching devices, each said switching device having a control terminal and an output terminal, first circuit means connecting the output terminals of said switching devices to one transformer winding portion, second circuit means connecting one output terminal of said rectifier means to said one transformer winding portion, a drive transformer having a core of linear low loss characteristics, the cross-section of said drive transformer core being less than one tenth the cross-section of said main transformer core, and a primary winding and two secondary windings on said drive transformer core, third circuit means connecting said primary winding to a second transformer winding portion, fourth circuit means connecting one drive transformer secondary winding to the control terminal of one of said switching devices, fifth circuit means connecting the other drive transformer secondary winding to the control terminal of the other switching device, said drive transformer and said fourth and fifth circuit means causing said switching devices of said inverter circuit to switch between cutoff and fully conducting states in response to saturation of said drive transformer core, the saturation characteristics of said drive transformer being coordinated with the saturation characteristics of said main transformer so that said drive transformer saturation causes switching of said inverter circuit switching devices without saturation of said main transformer core, and output terminal means for connecting an electric arc discharge device across a main transformer winding portion.
 16. The apparatus as claimed in claim 15 wherein said switching devices are transistors, each of which has base, emitter and collector electrodes, and further including means including a resistor having a value of less than five ohms connecting each emitter electrode to a common junction point, and imbalance means connected to the base electrode of one of said transistors for initiating operation of said inverter circuit.
 17. The apparatus as claimed in claim 16 wherein said output terminal means includes means for connecting a plurality of fluoroescent lamps across a main transformer winding and further including a plurality of secondary windings coupled to said main transformer for connection to filaments of the lamps, a capacitor connected across said main winding and coordinated with the inductive value of said main winding to modify the rate of voltage change, a plurality of output inductors connected to one terminal of said transformer main winding, each said output inductor having an inductive value of less than 20 millihenries. 